Studies on Synthesis, Characterization and Applications of Microencapsulation Process Via Interfacial Polymerization
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A SYNOPSIS OF THE THESIS ENTITLED Studies on Synthesis, Characterization and Applications of Microencapsulation Process via Interfacial Polymerization Submitted to GUJARAT TECHNOLOGICAL UNIVERSITY, AHMEDABAD For the Partial fulfilment of the Degree Of Doctor of Philosophy In CHEMICAL ENGINEERING Submitted BY Christian Ujvala Parsottamdas (Enrolment Number: 129990905004) Research Supervisor: Dr. Shrikant J. Wagh Principal, SHROFF S. R. ROTARY INSTITUTE OF CHEMICAL TECHNOLOGY Doctoral Progress Committee (DPC) Members Late Dr. Suhas A. Puranik Dr. Sachin Parikh Ex. Director, Environmental Cell, Professor in Chemical Engineering Atmiya University, Rajkot. Joint Director, DTE- Gandhinagar. CONTENT Sr. Title Page No. No. 1. Title of thesis and Abstract 3-4 2. Brief description on the state of the art of the research topic 4-6 3. Definition of the problem 6-7 4. Objective and Scope of work 7 5. Original contribution by the thesis 7-8 6. Methodology of research, Result/Comparisons 8-13 7. Achievements with respect to objectives 13-14 8. Conclusions 14 Copies of papers published and a list of all publications arising 9. 15 from the thesis 10. References 16 2 1. Title of thesis and Abstract Title of thesis: Studies on Synthesis, Characterization and Applications of Microencapsulation Process via Interfacial Polymerization Abstract: Microencapsulation is the technology of packaging of micronized solid particles, liquid droplets, or gas bubbles in microcapsules by applying thin film of coating or shell material. Resulting microcapsules are particles with diameters between 1µm to 1000µm.They have a core/shell structure which contains polymeric material as a wall (shell) enclosing the core. Synthesis of microcapsules is considered as microencapsulation process which can be categorized into two groups: (i) chemical processes like In-situ polymerization, Interfacial polycondensation, Interfacial cross- linking, matrix polymerization etc. and (ii) physical processes like spray–drying, pan coating, centrifugal extrusion, air-suspension coating etc. In this work, the generic Interfacial polymerization process is considered as Interfacial polycondensation (IP) that is step-growth polymerization reactions taking place at the interface. Interfacial polycondensation (IP), through several step-growth reactions, opens a wide window for synthesis of microcapsules (and membranes also) at ambient conditions without stringent conditions of monomer purity. IP is one of the important methods for synthesis of microcapsules. It offers advantages over other methods because it involves a chemical reaction between monomers dissolved in two different immiscible solvents. Variables such as nature of solvent, reactivity of monomers, types and concentration of surfactant, rate of chemical reaction, reaction conditions etc. play a vital role in deciding the characteristics of microcapsules produced. These give a great leverage over achieving the properties of microcapsules for certain pre decided applications, which may include encapsulation of pharmaceuticals, food additives, agrochemicals, solvents, adhesives, immobilization of living cells etc. The research work presented includes study of various aspects of microencapsulation via IP to form polymer shell, and release behaviour of certain encapsulated agrochemicals as active ingredients through polymer shell. The experimentation includes systematic study on synthesis of polyurea microcapsules under specific preparative conditions controlling the kinetic and mass transfer regimes of reaction to produce polyurea microcapsules as a tailor made product. Synthesis experimentation is 3 necessarily followed by characterization of the product formed. Various analytical tools like Fourier Transform Infrared (FTIR) Spectrophotometer, Differential Scanning Calorimeter (DSC), Scanning Electron Microscope (SEM), and X-ray Diffractometer (XRD) are used to characterize polymeric shell of microcapsules for its application of controlled/sustained release. 2. Brief description on the state of the art of the research topic: Interfacial polycondensation (IP) involves a chemical reaction between monomers dissolved in two different immiscible solvents [1]. Step growth polymerization reactions occur at, or in a thin region adjacent to the interface of the two immiscible phases, and since the polymer formed is insoluble in both the phases, accumulate at the surface of contact between the phases as shown in Figure-1[2]. IP is a heterogeneous process of mass transfer with chemical reaction and simultaneous occurrence of polymer phase separation and film formation [3]. The steady state concentration profiles of the monomers (Hexamethylene diamine and Hexamethylene di-isocyanate) used in a typical polycondensation reaction with concurrent phase separation of polyurea formed are shown schematically in Figure-1. Figure 1 Schematic diagram showing different regions of Interfacial Polycondensation 4 Where, A0a= unprotonated diamine concentration in bulk aqueous phase, A0ap= diamine concentration at aqueous phase-polymer interface, A0r= diamine concentration in reaction zone, AT = total diamine concentration in bulk aqueous phase, B0r= diisocyanate concentration in the reaction zone, B0s= diisocyanate concentration in the bulk organic phase, = partition coefficient of diamine between aqueous phase and polymer film and = partition coefficient of diamine between polymer film and organic solvent.[4,5] Interfacial polycondensation (IP) is one of the most widely used chemical processes for microencapsulation of agrochemicals as active ingredients for effective release to the target [6, 7]. As it happens with any product produced via a chemical reaction or a set of chemical reactions that the properties are determined by the reaction conditions and process variables, the synthesis of microcapsules loaded with active ingredient (AI) via IP is also governed by several physico-chemical factors and variables enlisted above in the abstract. The encapsulation of AI is mainly done for controlled/sustained release of AI, insecticides in this work, to obtain certain formulation. Thus it is a formulation technique that can offer multiple advantages stated below: Reduction of toxic effects. Enhancement of the duration of activity for an equal level of insecticide. Overall reduction in total consumption of insecticide. Reduction in evaporative losses. Protection of/from the external environment, and increase in use and handling convenience [8-11]. It is known from earlier works that polyurea synthesized by IP offers good flexibility in desirable properties of microcapsules for required release rates of active ingredient (AI) [12-13]. Various researchers have studied different operating parameters e.g. reactivity of monomers, types and concentration of surfactant, speed of agitation, different reaction parameters on reaction kinetics of synthesis of polyurea membrane by IP through experimental and modelling studies correlating rate of reaction with polymer film properties like film thickness, crystallinity and molecular weight distribution (MWD) [14-16]. 5 Study of the reported literature makes it clear that the IP reaction for synthesis of polyurea can be effectively used to make a polymer shell to encapsulate different core materials in it for controlled/sustained release. Several process conditions, such as monomer concentration ratio, phase volume ratio and number of moles of limiting monomer, and intrinsic properties like polarity of organic solvents and partition coefficient of aqueous phase monomer have significant effect on product properties. The available literature on polyurea synthesis via IP shows that sufficient experimental work is still required to prove legitimate claim of IP for making tailor-made polyurea microcapsules as a formulation for insecticides. The present work tries to address these issues and provides deeper insights. Study on effect of temperature on kinetics of IP and effect of a pendant group in solvent structure discussed in this work have not been covered by earlier workers. Experimental process followed and the variables studied in this work for the kinetic study (such as, bulk mole ratios of the monomers, R, the number of moles of limiting monomer per unit volume of dispersed phase, nL/Vd, and phase volume ratio, Vd/ Vc) are the integral part of the work as have been considered by earlier researchers. But, for experimental validation and corroboration purpose their values have been kept in similar range. However, a wide range of values has been studied to enable us to make certain conclusive remarks on microcapsules as a final product. Polyurea microcapsules were characterized by FTIR, XRD, DSC and SEM. After synthesis, towards application part of the work, release trends of three selected insecticides i.e. chlorpyriphos, cypermethrin (pesticides) and pretilachlor (herbicide) as a core material in polyurea shell were also studied. Encapsulation efficiency was calculated and rates of release of these insecticides into methanol was measured experimentally in controlled release experiments and reported. Semi crystalline polyurea shell material was synthesized and polymer crystallinity correlated with experimental variables and final applications i.e. encapsulation efficiency and release rate of insecticides. 3. Definition of the Problem: The present doctoral work entails the following studies: [1] To synthesize polyurea microcapsules via IP to study effect of different experimental variables like monomer mole ratio (R),